IMAGE: A spontaneous change of swimming direction by a single fish triggers a collective u-turn in a group of rummy-nose tetras (Hemigrammus rhodostomus).
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Credit: Jiang et al.

In a school of rummy-nose tetras, a common aquarium fish, group coordination appears to occur by each fish continuously changing which of its neighbors it pays attention to, according to new research published in PLOS Computational Biology.

The seamless group movements seen in some schools of fish and flocks of birds depend on individuals sharing directional information and changing direction based on each other's movements. However, it is unclear how many neighbors each individual pays attention to, and where they are located within the group.

To better understand these interactions, Li Jiang of Beijing Normal University, China, and colleagues from the Universities of Bristol, Roehampton, and Toulouse, studied schooling behavior in the rummy-nose tetra, a freshwater tropical fish. They developed a new method that combines behavioral analysis of live fish in a tank with computational modeling to reveal which neighbors each fish follows during collective school maneuvers.

The researchers had small groups of tetras swim in a ring-shaped tank so that their directional shifts would be obvious; clockwise versus counterclockwise. With the assumption that a brief time delay occurs whenever a fish reacts to a neighbor's movement (which has been well-studied), the scientists were able to identify which fish were influenced by which neighbors during collective group U-turns.

To refine their analysis, the research team also developed a computational model of the group U-turns that accounts for the fact that some movements that may appear to be coordinated could have just occurred by chance.

The analysis revealed that, during a group U-turn, a fish may intersperse phases in which its movement choices are affected by one or two influential neighbors with other phases during which its neighbors' movements are irrelevant. Group coordination appeared to occur by fish continuously changing whom they decided to pay attention to; not necessarily their closest neighbors.

"The ability to coordinate movements across a group without a leader confers a number of advantages, including efficient task partitioning and resilience to loss of a leader," Jiang says. "The rummy-nose tetra appears to have opted for a coordination strategy whereby any individual may become a leader depending on the need."

Next, the researchers plan to study how these interactions are combined at the individual level. Meanwhile, Jiang says, "Our findings could serve as a source of inspiration to optimize and automate a variety of man-made processes, such as swarms of drones in search and rescue operations."

Funding: LJ was funded by a grant from the China Scholarship Council (CSC NO. 201506040167). LG acknowledges support from EPSRC grant EP/I013717/1. RE has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 655235 "SmartMass". VL was supported by doctoral fellowships from the scientific council of the University Paul Sabatier. ZH was supported by the National Natural Science Foundation grants 61374165, 31261160495. This study was supported by grants from the Centre National de la Recherche Scientifique and University Paul Sabatier (project Dynabanc). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.

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